Calling methods from other classes using array objects in Java

Question

Why does this code not work? It seems I cannot set the variable to '10' with the Array, but with a normal object it works.

What am I doing wrong?

Class- 1

public class apples {
    public static void main(String[] args) {
        carrots carrotObj = new carrots();      
        carrotObj.setVar(5);        
        System.out.println(carrotObj.getVar());

        carrots carrotArray[] = new carrots[3];
        carrotArray[1].setVar(10);        
        System.out.println(carrotArray[1].getVar());
    }
}

Class- 2

public class carrots { 
    private int var = 0;
    public int getVar() {
        return var;
    }

    public void setVar(int var) {
        this.var = var;
    }
}

Console Output:

5
Exception in thread "main" 
java.lang.NullPointerException
    at apples.main(apples.java:17)

You need to fill the array with objects yourself. You get a NPE here: carrotArray[1] Also, use capital first letters for classes, i.e. Apples and Carrots — keyser
– keyser, Commented Jan 11, 2014 at 1:15
carrotArray[1] = new carrots(); before carrotArray[1].setVar(10);. — Elliott Frisch
– Elliott Frisch, Commented Jan 11, 2014 at 1:18

rgettman · Accepted Answer · 2014-01-11 01:15:33Z

1

You created an array, but when an array of objects is created, they are all initialized to null -- the default value for object reference variables. You need to create some objects and assign them to slots in the array.

carrots carrotArray[] = new carrots[3];

// Place this code
carrotArray[1] = new carrots();

carrotArray[1].setVar(10);

You could do something similar for position 0 and 2.

Additionally, the Java convention is to capitalize class names, e.g. Carrots.

answered Jan 11, 2014 at 1:15

rgettman

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Comments

le-doude · Accepted Answer · 2014-01-11 01:15:56Z

0

You need to initialize all the elements of the array; since they are not primitive data types their default value is null.

carrots carrotArray[] = new carrots[3];
for(int i=0; i < carrotArray.length; i++){
   carrotArray[i] = new carrots();
}
carrotArray[1].setVar(10);

System.out.println(carrotArray[1].getVar());

answered Jan 11, 2014 at 1:15

le-doude

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